Brown bears (Ursus arctos) are the bears of legend. People often hear the terms brown bear and grizzly bear used interchangeably and rightfully so. The two names describe the exact same animal. NPS staff from different national parks say that there is a tendency to refer to the bear that lives in the interior as a 'grizzly' and its coastal inhabitant as a 'brown bear'. The real difference is as a result of food supply. Coastal bears have greater access to supplies of protein obtained through feeding on salmon while brown bears in the interior have a diet that lacks this specific protein resulting in smaller bears with lighter coats.
There are two main ways to distinguish a brown bear from a black bear: size and the appearance of a 'shoulder hump'. In contrast to the black bear, brown bears have a shoulder hump and a "dish-shaped" or concave face. In addition, brown bears greatly exceed black bears in physical size - leading to easier track identification when in mixed bear country.
Size and Life Expectancy of Brown Bears: Adult brown bears stand approximately 3.5 feet tall when on all fours, and have a body length of just over seven feet. Bears can exceed eight feet tall when standing on their hind legs. They can be seen exhibiting this standing behavior to follow scents and get a broad lay of the land. Due to less than stellar vision, the brown bear relies on its intense sense of smell for navigation. The weight of brown bears varies greatly throughout the year. Bears are leaner in the spring or early summer when they emerge from hibernation. They gain weight steadily throughout the summer and begin to extend feeding hours pre-hibernation up to 20 hours a day - leading to rapid weight gain. These fat stores will bring an adult male's weight to between 500 and 1000 pounds with some mature adult males easily exceeding a ton or more. Females, on the other hand, will weigh anywhere between 300 to 600 pounds in the fall before denning.
For their size and lumbering appearance, brown bears are deadly quick. They can achieve short bursts of up to 35 miles per hour and can detect the scent of food from a mile away. They are one of nature's most perfect predators whose only natural enemy is man. In perfect wilderness conditions, brown bears can live past 30 years but general life expectancy in males is around 20 and females around 25.
Habitat and Range: Brown bears occur throughout Alaska, western Canada and the northwestern United States / Rocky Mountain region including Washington, Montana and Wyoming. The home range of a brown bear is extremely dynamic and varies with territory but averages around 300 square miles per bear. The more concentrated the food sources, the smaller the range necessary to maintain the animal. For example, adult male brown bears living in the Brooks Range of Alaska have an average home range of approximately 521 square miles. However, brown bears living in the salmon-rich coastal areas, require only about 10.5 square miles. Because brown bears don't normally care to defend their home ranges, there is inevitable overlap in brown bear territory.
Food and Survival Strategies: Brown bears are opportunistic feeders, fond of any carrion and often found eating garbage in human dumps. Typically they eat more than 75 percent vegetable matter consisting of berries, flowers, grasses, herbs, and roots. The remaining 25 percent consists of decaying carcasses, fish, insects, elk and moose calves, and a variety of other small mammals. Due to their large size, brown bears require a very high caloric intake of food. In order to achieve this, brown bears will eat 80 to 90 pounds of food per day in the summer and early fall. During this eating binge, in preparation for hibernation, brown bears are able to gain three to six pounds of fat each day. Hibernation lasts from five to eight months in the coldest parts of the brown bear's range. However, in warmer areas, like Kodiak Island, some bears may remain active throughout the winter season.
Reproduction and Young: Female brown bears normally become sexually mature at five or six years of age, their average litter is two cubs and the interval between litters is three to four years. Mating occurs between late May and early July. Females are capable of delayed implantation. If a female does not have enough fat reserves for the winter the embryo will not implant and simply be reabsorbed. Sometime around the denning period, the embryo will attach itself to the uterine wall and after a period of eight weeks (January or February), the cubs will be born while the mother is still in hibernation. At birth, the cubs are blind and hairless, and very tiny--weighing less than a pound. They are able to move sufficiently to suckle on their mother who remains asleep. Her milk is very rich (over 20 percent fat), allowing the cubs to gain weight quickly in preparation to leave the den in April or May.